This invention relates to a process for preparing alkyl-extended piperazines, such as 1,4-diethylpiperazine, and alcohol-extended piperazines, such as N-(2-hydroxyethyl)piperazine. This invention also relates to a process for preparing amine-extended piperazines, such as N-(2-aminoethyl)piperazine, bis(piperazinyl)alkanes, and oligo(piperazinylalkanes).
Alkyl-extended, alcohol-extended, and amine-extended piperazines are useful intermediates in the preparation of melt adhesive polymers and fine industrial chemicals, including veterinary antihelmintic pharmaceuticals, insecticides, and high temperature lubricating oils.
U.S. Pat. No. 3,364,218 teaches the self-condensation of N-(2-hydroxyethyl)piperazine to poly-1,4-ethylenepiperazine in the presence of hydrogen and a solid acid catalyst, such as silica-alumina, alumina, tungsten oxide, aluminum phosphate, and acid clays. It is difficult to control the degree of polymerization in this process. Accordingly, it is difficult to obtain high yields of N-(2-aminoethyl)piperazine, 1,2-bis(piperazinyl)ethane, tris(piperazinylethane), or other lower oligo(piperazinylethanes). Moreover, cyclic compounds, such as 1,4-diaza-[2.2.2]-bicyclooctane, are produced as undesirable by-products. In addition, the catalysts employed in this process lose their physical integrity in the presence of amines and water; therefore, the process is hampered by catalyst losses and separation problems.
U.S. Pat. No. 4,552,961 discloses a process for the preparation of polyalkylene polypiperazines comprising reacting piperazine with alkylene glycols or alkanolamines in the presence of a catalyst of phosphorus amide. Disadvantageously, this catalyst is homogeneous and must be separated from the product stream.
It would be advantageous to have a catalytic process for preparing alkyl-extended, alcohol-extended, or amine-extended piperazines. It would be more advantageous if the degree of polymerization of such a process could be controlled, and selective alkyl-extended, alcohol-extended or amine-extended piperazines could be prepared in high yields. It would be even more advantageous, if the catalyst for such a process was insoluble in the reaction mixture. With an insoluble catalyst the problems of leaching, plugging, and catalyst separation would be avoided, and the amination process would be more suitable for industrial adaptation.